TREES AS CROPS IN ALASKA PROFILE
WITH AN EMPHASIS ON SPRUCE
Revised 2009
Robert A. Wheeler
Thomas R. Jahns
Janice I. Chumley
PRODUCTION FACTS
Growing trees in Alaska can be difficult. This
document addresses basic questions regarding
growing tree seedlings as an agricultural crop.
Whether growing a few seedlings or thousands,
many of the basic production questions are the
same.
From the standpoint of tree seedling production
there are three basic regions in Alaska:
Southeast, South Central, and the Interior.
Producing high quality tree seedlings is
achievable in all three regions however care must
4-H Tree Sale in Soldotna, AK May 2003
(photo/Bob Wheeler).
be taken to match tree species requirements with
local environmental conditions. Through the
efforts of the University of Alaska Fairbanks and the Agriculture and Forestry Experiment
Station, many tree species have been evaluated over the past 100 years for their performance.
Results from these species trials have led to the listing of tree species, growth characteristics,
and site requirements found in Table 1.
DEMAND
Interest in tree production can vary from growing trees for your yard or property to full scale
outdoor or greenhouse, bareroot, or container nurseries. Tree planting and tree sales continue
to be of considerable interest to the public although there are no large-scale commercial tree
nurseries currently operating in Alaska. A state tree nursery was once operated in the
Matanuska Valley area, but it has been closed. Reasons for the closure were based upon the
high cost of producing seedlings in Alaska versus what it would cost to import them from
nurseries outside the state and also, the overall operational difficulties and risks associated
with an Alaska nursery program. This has resulted in the demand for seedlings being met
largely by Canadian and northwestern U.S. producers.
Estimates of annual planting demand are difficult to determine due to the number of nurseries
contracted. Over 40,000 seedlings are estimated to be planted on private property (non-native
corporation lands) in Alaska annually. The demand for seedlings has been further enhanced
by the efforts of the Anchorage and Kenai boroughs to reforest forestland devastated by the
spruce bark beetle. As a result, current contracts are underway to produce more than 1 million
1
The Crop Profile/PMSP database, including this document, is supported by USDA NIFA.
seedlings. Additionally, it is estimated that more than 40,000 woody shrubs are planted
annually in Alaska by private landowners based upon statistics from out-of-state nurseries.
In addition to tree seedlings for reforestation, Christmas tree sales account for over 50,000
trees sold each year, statewide. Christmas tree plantations have been attempted in Alaska
with limited success. A typical Christmas tree of the 6-7 foot class will take about 8-12 years
to develop. Christmas tree species for Alaska plantations include lodgepole pine, Scotch pine,
jack pine, Siberian fir, and Colorado blue spruce.
Helpful References: (see reference #1, 2, 3, and 4)
TREE PLANTING BY REGION
Recent research has shown that northern latitudes such as those found in Alaska are
particularly more impacted by global climate change than those found in the tropics. This
climate change in Alaska has resulted in a substantial increase in growing season and growing
conditions suited for non-local species. However, in spite of these increasing site
temperatures and agricultural zone re-classifications, the phenological response of these plants
to photoperiod has not changed since there has been no relative change in photoperiod. Plants
from more southerly locations that may be now adapted to prevailing climate conditions but
not to the extended summer daylight may find their phenological response to initiate the onset
of winter hardiness is not being triggered as needed in order to enhance their winter survival
ability. Consequently, for a given location, it is strongly suggested that a multi-year testing
period be conducted in order to determine the survival and growth of non-local species. This
is particularly true for species that are being moved from southern to more northern locations.
Many non-local but boreal forest species such as Siberian larch, Lodgepole pine, and Siberian
fir have performed exceptionally well in Alaska whereas Ponderosa pine and Douglas fir from
more southern locations are not well adapted to Alaska although they can be found on cold
sites in their native habitat which may reflect some photoperiod sensitivity. Although there
may be substantial changes in local plant hardiness zones with warming climate conditions,
phenological responses to prevailing photoperiods may limit our ability to establish some nonnative tree species in Alaska.
Tree hardiness zones have been developed for Alaska and are summarized in the following
diagrams. These hardiness zones can be used to help select tree species for your area by
matching the hardiness zone recommendations with species of interest.
2
NON-NATIVE AND NATIVE TREE SPECIES GROWTH COMPARISONS
Considerable interest and concern has been expressed in recent years regarding the planting of
non-native tree species in Alaska. Concern for the accidental release of invasive plants has
lead to the development of Invasive Species Lists for Alaska. Although most tree species
would not likely become noxious or invasive in nature it is helpful to know what species
might be of concern. Dr. John Alden, in his report on Naturalization and Growth of Nonnative
Conifers in Alaska, indicated that 20 year height and diameter growth of both lodgepole pine
and western Siberian larch were significantly greater than that for white spruce when grown
on the same site (Ref.#1). The average height growth of the white spruce was exceeded by
Siberian larch, lodgepole pine, Scotch pine, jack pine, Dahurian larch, paper birch, and balsam
fir. There is some evidence to suggest that the growth of white spruce may eventually exceed
some of the early fast growing species, but more research is needed. Dr. Alden estimates that
lodgepole pine and Siberian larch will soon become established as naturalized non-native
conifers in Alaska. For a list of non-native and invasive plants in Alaska contact your local
Alaska Cooperative Extension Service office or the web site established by the Alaska
Committee for Noxious and Invasive Plants Management at www.cnipm.org.
3
Table 1: Listing of Trees Adapted to Alaska Environments (Ref #11)
Species
Common Name
Hardiness
Height (ft.) Seeds per lb. Pre-germination
Abies concolor
White fir
SC, SE (Zone 3)
30–130
11,100
Abies lasiocarpa
Subalpine fir
SC, SE (Zone 2)
20–80
34,800
Abies sibiric
Siberian fir
INT, SC, SE (Zone 1)
80
unknown
Chamaecyparis
nootkatensis
Alaska yellow cedar
SC, SE
(Zone 4)
40-100
108,000
Larix decidua
Larix gmelinii
Larix laricina
Larix russica
(sibirica)
Picea abies
Picea englemannii
European larch
Dahurian larch
Eastern larch
Siberian larch
SE, SC (Zone 2)
INT, SC, SE (Zone 1)
INT, SC, SE (Zone 1)
INT, SC, SE, W (Zone 1)
30–70
60–70
40–80
40–100
70,000
120,000
318,000
44,000
Norway spruce
Englemann spruce
SC, SE (Zone 2)
SC, SE (Zone 2)
100–200
100–165
64,000
135,000
Picea glauca
Picea mariana
Picea pungens
White spruce
Black spruce
Colorado Blue spruce
INT, SC, SE, W (Zone 2)
INT, SC, SE, W (Zone 2)
SC, SE (Zone 2)
40–115
15–70
80–150
226,000
404,000
106,000
Picea sitchensis
Sitka spruce
SC, SE (Zone 7)
80–225
210,000
Picea x lutzii
Pinus albicaulis
Lutz spruce
White-bark pine
SC, SE (Zone 3)
SC, SE (Zone 3)
55–100*
20–100
200,000+
2,600
Pinus aristata
Bristlecone pine
SC, SE (Zone 3)
8–50
18,100
Pinus banksiana
Jack pine
INT, SC, SE (Zone 2)
35–100
131,000
Pinus cembra
Swiss Stone pine
INT, SC, SE (Zone 4)
30–70
2,000
Pinus contorta
var. latifolia
Pinus contorta
var. contorta
Pinus flexilis
Lodgepole pine
INT, SC, SE, W (Zone 5)
30–80
94,000
Shore pine
SE (Zone 7)
20–30
135,000
Limber pine
INT, SC, SE, W (Zone 2)
20–80
4,900
Pinus mugo
Pinus sibirica
Pinus sylvestris
Mugo pine
Siberian stone pine
Scotch pine
INT, SC, SE, W (Zone 2)
INT, SC, SE (Zone 3)
INT, SC, SE (Zone 2)
6–40 feet
50–90 feet
60–130
69,000
1,800
75,000
Pseudotsuga menziesii Douglas fir
var. menziesii
Thuja occidentalis
Northern white cedar
Tsuga heterophylla Western hemlock
SC, SE
(Zone 4)
SC, SE (Zone 2)
SC, SE (Zone 6)
150-200
39,500
40–100
100–150
346,000
260,000
Tsuga mertensiana
Mountain hemlock
SC, SE (Zone4)
25–125
114,000
Conifers:
28 days on moist
medium at 34–41˚
28 days on moist
medium at 34–41˚
28 days on moist
medium at 34–41˚
moist medium for
30 days at 68˚ F
followed by 30 days
at 40˚ F
None required
None required
None required
None required
None required
30 days at 34–41˚ F
after soak for 24 hours
None required
7 days at 41˚ F in water.
30 days on moist
medium at 34–41˚ F
2 days on moist
medium at 34 –41˚ F
None required
90 days on moist
medium at 34–41˚ F
30 days on moist
medium at 34–41˚ F
7 days on moist
medium at 34–41˚ F
90 days on moist medium
at 34–41˚ F after mech.
scarific.
30 days on moist medium
20 days on moist
medium at 34–41˚ F
30 days on moist
medium at 34–41˚ F
None required
Cold moist stratification
30 days on moist
medium at 34–41˚ F
21 days on moist
sponge at 32–41˚ F
None required
21 days on moist
medium at 34–41˚ F
90 days on moist
medium at 34–41 ˚F
Deciduous:
Acer glabrum
var. douglasii
Acer negundo
Douglas maple
SC, SE (Zone 3)
20–30
13,400
Boxelder maple
SC, SE (Zone 2)
30–75
13,400
Acer platanoides
Norway maple
SC, SE (Zone 3)
40–100
2,800
Acer rubrum
Acer saccharinum
Red maple
Silver maple
SC, SE (Zone 3)
SC, SE (Zone 3)
40–90
50–90
22,800
1,780
Warm followed by
cold strat.
60 days on moist
medium at 34–41˚ F
90 days on moist
medium at 34–41˚ F
None required
None required
4
Acer tataricum
Tatarian maple
SC, SE (Zone 3)
15–20
11,300
Acer tataricum
var. ginnala
Alnus crispa
Alnus sinuata
Amur maple
INT, SC, SE (Zone 2)
multi-stem
unknown
Mountain alder
Sitka alder
INT, SC, N (Zone 2)
INT, SC, SE, W (Zone 2)
Alnus tenuifolia
Betula glandulosa
Betula nana
Betula papyrifera
Betula pendula
Cornus canadensis
Thinleaf alder
Shrub birch
Dwarf arctic birch
Paper birch
European white birch
Dwarf dogwood
3–13
5–40
multi stemed
INT, SC, SE (Zone 2)
15–30
INT, N, SC, SE, W (Zone 1) 1–10 ft.
INT, N, SC, SE, W (Zone 2) 3–5 ft.
INT, SC, SE, W (Zone 2 )
20–80 ft.
SC, SE (Zone 2)
40–50 ft.
INT, SC, SE, W (Zone 2)
3–12 inches
675,000
3,839,000
unknown
380,000
795,000
67,000
Cornus stolonifera
Red-osier dogwood
Cotoneaster
Peking cotonester
acutifolius
Crataegus succulenta Fleshy hawthorn
Fraxinus
Green ash
pennsylvanica
Malus sp.
Apple varieties
INT, SC, SE (Zone 2)
INT, SC,SE(Zone4)
3–12 feet
5-8 ft.
18,500
24,194
INT, SC,SE (Zone3
SC,SE (Zone3)
25 ft.
50-60 ft.
20,600
17,260
INT,SC,SE (Zone 3)
10-25 ft.
up to 60,000
Populus balsamifera
Populus tremulides
Populus trichocarpa
Prunus maackii
Prunus virginiana
Pyrus ussuriensis
Sorbus acuparia
INT, N,SC,SE, W(Zone1)
INT,SC,SE (Zone1)
SC,SE (Zone 3)
INT,SC,SE (Zone2)
INT,SC,SE (Zone 2)
INT,SC, SE, (Zone 3)
INT, SC,SE, W (Zone 2)
30-50 ft.
40-80 ft.
80-100 ft.
35-45 ft.
20-30 ft.
30-40 ft.
15 ft.
unknown
3,600,000
300,000
Cold strat. for 4-5 mo.
warm strat. for 60 days
and cold for 6 months
30 days alter. warm
days and cold nights
None required
None required
None required
4,790
9,100
Unknown
Cold strat. for 3-4 mo.
Cold strat. 38oF for 60 days
Cold strat. for 2-4 months
Balsam popular
Quaking aspen
Black cottonwood
Amur chokecherry
Chokecherry
Ussurian pear
European mtn. Ash
1,280,000
unknown
90 days on moist
medium at 34–41˚ F
90 days on moist
medium at 34–41˚ F
60 days on moist
60 days on moist
medium at 34–41˚ F
None required
None required
unknown
None required
None required
Cold stratification
for 3–4 months
Cold stratification
Cold strat. for 1-3 mo.
TREE NURSERY SITE ASSESSMENT —
WHAT ARE THE CONDITIONS? (Ref. #9)
Selecting an outdoor bareroot nursery site requires attention to the environmental conditions
and fluctuations that may occur year-round. Problems with seedling mortality caused by
insects, diseases, and environmental conditions can be minimized by careful consideration of
site conditions. To produce economical high-quality seedlings for sale to the public, careful
attention to site conditions is essential. Tree seedlings can be impacted by both biological
(biotic) and non-biological (abiotic) factors (Table 2). When considering a location for
seedling production, concern should be given to these factors.
Table 2: Listing of Biological and Non-biological Factors Effecting Nursery
Site Selection
Non-biological Factors:
Biological Factors:
Cold Temperatures: Cold or frozen soils and permafrost or
partial permafrost conditions. Be concerned about slope aspect
and elevation and precipitation patterns. Frozen soils at times of
lifting or root pruning could result in damage to seedlings
Fungal infections including evidence of root rots, molds, and
other related fungal conditions affecting roots and leaves. Avoid
boggy wetlands or poorly drained soils.
Wind: Exposed areas with high wind potential should be
avoided. Wind can be a cause of several problems including
excessive moisture stress and mechanical damage to seedlings.
Bacteria and viruses that can cause mortality or defoliation.
Avoid species that are known to be highly susceptible. Seedlings
can be very susceptible to damping off disease and other
disorders that can destroy large numbers of trees.
Soil Condition: Poor quality soils with nutrient deficiencies,
high or low pH, salt. Be sure to do soil sampling for the entire
plantation area. Soils low in N and other nutrients can be
augmented if necessary. Be careful of poor drainage that may
cause contamination such as by salt from roads. Avoid areas of
low pH below 4.0 or exhibiting metal toxicity.
Areas of high moose browse can cause severe damage unless
fenced and controlled. Damage by browsing animals can cause
loss of trees and value.
Consider how you will control pests, possibly by fencing.
5
Mechanical injury: Muddy or boggy soils may cause machinery
problems that could cause damage to seedlings. Coarse textured
sandy soils are best for lifting seedlings without damaging the
root systems.
Birds that can consume seed and damage seedlings. Does the
area have a bird problem?
Heat: Avoid sites with excessive heat exposure which may cause
problems with costs for irrigation and associated plant moisture
stress and loss of seedling growth.
Weeds and weed control measures. Be aware of herbicide and
pesticide application limitations for the nursery area.
Avoid droughty or water logged soils: Excessive moisture stress
a wet root condition can cause seedling mortality. Wet soils are
also sources of fungal infections.
Alaskan forest soils can be prone to mosses and algae that can be
damaging to seedlings or difficult to control.
Improper species selection for Alaskan day length. Variety not
suitable for northern photoperiod.
Colorado Blue Spruce bareroot
(photo/Bob Wheeler).
Colorado Blue Spruce in pots
(photo/Bob Wheeler).
AN EXAMPLE OF HIGH QUALITY SPRUCE SEEDLING PRODUCTION
If you are interested in producing commercial quality seedlings for sale in Alaska you should
consult with the American Standards for Nursery Stock which was originally published in
1923 by the American Nursery and Landscape Association. The latest edition of the standards
is ANSI Z60.1-1996 and is available upon request directly from the ANLA or their web site
http://www.anla.org/.
Seeds for Planting: There are several national and international seed companies that can
provide seed for growing seedlings. However, care must be taken to consider the source of
the seed and whether or not it is certified seed. Certified seed has documentation for proof of
source location to further assist in determination of seed origin and seed zone classification.
Variations in local and regional environmental conditions limit where seeds can be grown
successfully. Variations in climate and environment throughout a region are the basis for the
development of seed transfer zones. Some rules to follow regarding seed collection include:
1.
Maintain a record of the source location of the seed used. Include
the seed zone, latitude/longitude, aspect, and elevation of the seed source and
keep this information on a tag with the seed storage bag at all times.
2.
Collect seeds from at least 30 well distributed and high-quality trees
throughout the area of collection.
6
3.
Try to collect seeds from sites similar to where you will be planting
them (features including elevation, soil type, latitude, amount of moisture
available, and aspect).
4.
Try to avoid transfer of seeds from upland areas to lowland or
riparian sites and vice versa. Try to avoid transfer of seedlings
beyond natural barriers such as mountain ranges or above treeline.
5.
Restrict seed transfer to within 500 feet in elevation of the
collection source.
COLLECTING SEEDS
White, Sitka, and black spruce cones all mature in
the fall (late August through September) in
Alaska. Squirrels collecting cones can be an
indicator of seed ripeness. However, you can
better estimate seed ripeness by cutting several
cones in half lengthwise and examining a cross
sectional cut through the seeds. Seeds with
embryos extending at least 80-90 percent of the
length of the seed cavity are considered to be
sufficiently ripe to be viable.
Care in collecting tree seed is important since
molds and excessive moisture and/or high
temperatures can damage the ability of seeds to
germinate. Also, care should be taken to assure that the cones are not collected too early,
since this can significantly reduce seed viability. If the cones are collected too late, many of
the good seeds may have already been shed, since the cone scales open during cone ripening
releasing the seeds.
White spruce canopy with cones
(photo/Bob Wheeler).
Tree seeds can be collected from standing
trees, felled trees, or from squirrel caches.
The seeds can be stored on racks in open
mesh bags such as gunny sacks that allow the
cones to dry while limiting the formation of
molds. Each bag should be carefully tagged
with information about the species, location
of collection, and date of collection of the
cones. The bags of cones should be filled
only half full and should be stored in a
covered, dry, well-ventilated location. A few
weeks to a month of drying, depending on
environmental conditions, will be required before the cones open to release the seeds. Collect
and cleanse the seeds using a screen box to sift debris from the cone bags and isolate the tree
seeds.
7
Seeds should be dewinged and stored in dry plastic bags or sealed containers and refrigerated.
The containers must be sealed against moisture.
SEEDLING PRODUCTION
Tree seedling producers must make a choice
whether to produce bareroot seedlings using
native soils in an outdoor environment or
whether to produce container seedlings planted in
artificial medium usually under controlled
environmental conditions in a greenhouse.
Bareroot seedlings will tend to have larger, more
developed root systems and can be grown inplace for two or more years before outplanting.
Culturing techniques such as bed wrenching and
root pruning can be used with bareroot stock to
enhance the quality and mass of roots and modify
White spruce in square pot containers
(photo/Bob Wheeler).
the shoot to root ratios. However, Alaskan
environments can create problems for bareroot
nurseries due to the short growing seasons and cold soils, which can make it difficult to
manage and lift seedlings at needed times.
Container seedlings have several advantages over bareroot stock. These include ease of
processing seedlings for mass production and development of uniform seedlings that are
easier to plant in harsh environments and the convenient, controlled application of
mycorrhizal inoculation of root systems. Container seedlings are more easily grown inside
greenhouses where it is easier to control day and night temperature regimes, day length and
light intensity, watering and fertilizing, and carbon dioxide concentrations. Some drawbacks
of container seedlings are that they are more prone to frost heave, they tend to be a smaller
seedling at outplanting than bareroot seedlings, they have a higher potential for root binding,
and they may be prone to more transplant shock and moisture stress.
There are a number of forest tree seedling containers on the market, several of which have
been used in Alaska and generally occur in the form of either: 1) plastic tubes, 2) styrofoam
blocks, or 3) pre-formed plugs. Nurseries and greenhouses can be contacted to purchase
supplies of these container types. Tree containers vary greatly in size and design depending
upon the size of the seedling being produced, root system developed, and planting medium
being used. Commonly used tree containers include the Ray Leach Single Cell (tubes), plastic
dibble tubes, styrofoam blocks, and Spencer-Lemaire Root Trainers.
When transferring the container seedlings to the field for planting, it is common to remove the
tree seedlings from their containers, wrap them in plastic wrap and transport them in a damp
and shaded enclosure or bag to the field for planting.
GROWING MEDIUM FOR CONTAINER SEEDLINGS
There are many alternative potting mixtures available for planting seed or seedlings in
8
containers. Commercially prepared media are available in convenient bulk wrapped cubes but
are more expensive than self-prepared media which can be easily made from ingredients
available at most commercial nursery/greenhouse retailers. Commonly used mixtures include
1 to 3 parts of medium textured peat moss to 1 part coarse to medium horticultural grade
vermiculite mix. Also use of 0.3 to 0.5 parts Perlite can be added to the mixture, as well as
fertilizer and micronutrients. The addition of magnesium sulfate or Dolomitic lime may also
be needed, however too much can cause seedling nutrition problems. Conifer species prefer an
acidic soil pH which also helps to reduce seedling losses to damping-off disease. Growers are
cautioned that mineral soil should never be used for container media.
SEEDLINGS AND TEMPERATURE CONTROL
Cold stratification of tree seeds, a practice used to enhance germination success has been
found to not be necessary for white and black spruce and fresh lodgepole pine seeds (stored
lodgepole pine are recommended to have a 30 day pretreatment of 33o to 41oF on moist
medium).
Conifer seeds will germinate best in 60 o F to 70o F conditions. Germination of seed will be
inhibited if temperatures exceed 75oF. After the seedlings emerge, the recommended
temperatures for seedling growth are 750F to 800F during the light period (day), and 650F to
700F during the dark period (night). Temperatures above 850F to 900F will inhibit seedling
growth and survival. Care must be taken to assure that sufficient air circulation is provided for
greenhouse environments. For guidance on germinating tree seeds consult the pregermination requirements shown on Table 1 or consult Ref #4.
Maintaining proper temperatures for growing seedlings is especially critical for young
seedlings. Excessive temperatures can lead to plant moisture stress along with the shutting
down of photosynthesis under higher temperatures and increased respiration energy costs.
Higher temperatures in greenhouses can be controlled by venting (by convection or fan driven
or by use of a water-cooled baffle system) to draw moist air into the greenhouse which
provides cooling by evaporation. Alternatively, cooling can also be achieved by use of
shading or use of shade cloths to cover the seedlings or greenhouses to increase reflectance of
solar radiation. A variety of materials can be used to provide shade including wooden lath
and shade cloths.
Examples of temperature control are provided by Table 3 (Ref. #7).
Table No. 3 : Example of Temperature Control by Use of a Shade Cloth
Light Intensity
Shading
Type
No Shading
50% Shade
Cloth
Air
Temp.
Leaf
Temp.
Leaf
Temp.
(ft-candles)
(0C)
Air
Temp.
1,370
70,200
36
97
40
105
525
27,000
32
90
32
90
(Micromoles/
2
s/m )
Light
Intensity
(0F)
(0C)
(0F)
Additionally, cooling of seedlings especially within greenhouses can be achieved by use of a
short burst of mists during the hottest period of the day. Combining misting with the use of
9
light colored mulch rock or material can effectively help to control heat damage to the stem
area of the seedling.
Young seedling losses due to damping off syndrome can be a serious problem resulting in
significant losses of seedlings (see pest control section).
Once the seedlings have grown to 8 inches tall, gradually reduce the growing temperatures 5
to 10 degrees per week (especially if possible during the dark period) in order to prepare them
for being transplanted. Reduced temperatures, shorter day lengths (photoperiod), and perhaps
lower light intensities are necessary to induce dormancy and the hardening of seedlings for
eventual transplantation. Cool temperatures and even mild frost during the night periods can
be beneficial to completion of the hardening process for over-wintering container grown
seedlings.
ILLUMINATION REQUIREMENTS
Conifer seeds germinate well at low light intensities and germination can even occur in full
darkness. The minimum photoperiod and light intensity recommended for the seedling
emergence phase at latitudes north of 600 are 20 hours at 350 micromoles/m2/sec or 1/3rd full
sun light. Optimum average light intensities are likely in the 900-1200 micromoles/m2/sec
range during the period of rapid seedling growth. Maximum outdoor light intensity on a clear
day in mid June at Fairbanks is about 1800 micromoles/m2/sec. Consequently, if possible, it
is recommended that some form of shading be used to control light intensity by as much as
30%. Various shade cloth materials are available for use in shading which vary depending
upon the thickness and color of the cloth. Germinating seedlings are especially susceptible to
high light intensities and may require additional shading to further reduce light down to the
level of 200-350 micromoles/m2/sec before being placed under higher light intensities during
their rapid growth phase.
Once the seeds have germinated and the seedlings begin the period of rapid elongation
(usually lasting about 60 days) it will be necessary to maintain a 20 to 22 hour light period.
As the time approaches for outplanting or hardening it will be necessary to reduce the
photoperiod back to between 12 and 16 hours. Most nurseries harden seedlings under natural
conditions of light and temperatures. Artificial darkness is often required to reduce
photoperiods and harden low latitude seedlings (seeds derived from southern latitudes) during
late summer at high latitudes (600 to 680 North). The problem of growth cessation, dormancy,
and winter hardening of stock in the nursery is avoided if the seedlings can be transplanted to
the field by June or early July (Ref. #11).
FERTILIZER RECOMMENDATIONS
Bareroot seedlings (seedlings grown and
managed in field soils): Fertilizing seedbeds is
very important to maintain the health and vigor
of your seedlings. Applications of fertilizer can
be made either by top dressing over the seedbed
or by incorporating it directly into the planting
media. You will need to determine how much
and what kind of fertilizer is needed. Both
nitrogen (N) and potassium (K) are soluble and
10
Colorado blue spruce bareroot (photo/Bob
Wheeler).
can be carried to the root zone of the seedlings via the irrigation water and consequently can
be spread on the surface of the seedbed. Phosphorus (P) is much less soluble and so must be
incorporated into the soil in granular form or applied as liquid fertilizer.
Once the seedlings have emerged and grown beyond 8 centimeters (3 inches) you will need to
apply an application of a balanced formula fertilizer such as 10:10:10 (N:P:K) at the
recommended rate of 7 ounces per 100 square feet of bed space (Ref.#1). This should be
applied twice in the summer (ie. June and July) but discontinued after July 15th. You will
need to apply water immediately after fertilizing to flush off any fertilizer adhering to the
foliage and facilitate its transport to the root zone. Intensive fertilization schedules are
available for bareroot seedlings, depending upon soil pH. For soils that are acidic or have
pH’s less than 7.0 you should select ammonium phosphate (11:52:0) If you have basic soils
with pH’s higher than 7.0 then you should use ammonium sulfate (21:0:0:26) as your nitrogen
source which will also help to lower the soil pH over time.
Trays of 6 month old western red cedar
seedlings in a greenhouse (photo/Bob
Wheeler).
Container Seedlings:
Fertilizer recommendations for container seedlings can vary depending upon the soil medium
characteristics such as pH. Commercially prepared soil mediums commonly include a starter
fertilizer incorporated in the medium.
For preparing self-mixed growing medium, slow release fertilizers such as Osmocote (17-712) are suggested along with additions of MagAmp and Micromax for macronutrient and
micronutrient needs. The practice of nutrient loading is commonly used to reduce
transplanting shock by apply fertilizer after the seedlings enter dormancy and before being
outplanted.
SEEDBED DEVELOPMENT AND PLANTING RECOMMENDATIONS
Bareroot tree nurseries generally use raised seed beds (ie. 4 feet wide and raised 3 to 6
inches). This approach promotes better soil drainage and soil warming. Wet soils can
contribute to damping off and other diseases for the developing seedlings.
Seeds are usually sown in rows at a density such that each seedling will be able to grow
without excessive competition. This approach also makes it easier to monitor and achieve
uniform seedling survival and growth. Seedling rows are commonly planted at 6 inches or 12
inches between rows for the production of 2+0 seedlings (trees grown for two years in the
same seed bed without being transplanted to a transplant bed). A general goal for seed bed
density is to achieve approximately 25 seedlings per square foot with seedling spaced about 1
to 1.5 inches apart. Consideration must be given seed germination rates that are less than
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100% so that additional seeds are planted to account for losses in seed germination. For
example, if seed germination rates are only estimated to be about 65% then instead of planting
25 seed per square foot as would be used for 100% germination, you would need to plant
about 38 seeds per square foot. You may need to test your seed to determine germination
rates before planting your nursery beds (Ref # 8). Germination rates can decline rapidly with
older stored seeds.
IRRIGATION OF SEEDLINGS
To maximize seedling growth, photosynthesis, and seedling vigor it is necessary to minimize
the level of plant moisture stress in the seedlings caused by inadequate irrigation, high
temperatures, and excessive seedling transpiration. Watering is important, but don’t oversaturate the soil, as excessively wet soil can promote pathogenic fungi, especially “dampingoff”. Initially, it is best to provide repeated light mistings. Once the seedlings have emerged
and grown approximately one month, you can begin to irrigate the soil deeper, but not
excessively. Watering can be done with an oscillating yard sprinkler as long as a consistent
application of water is achieved. Drip irrigation and permanent sprinkler systems can be more
effective in giving even applications of water, but may involve more cost and maintenance. A
soaker hose can also be effective at providing irrigation water to the seedlings, although their
delivery is often uneven at best.
Transpiration losses increases rapidly as the seedlings grow larger, increasing the potential for
moderate to heavy plant moisture stress. It will become necessary to irrigate more frequently
with multiple applications per day. As you begin to get closer to the time of transplanting or
outplanting, you will want to develop some hardiness in the seedlings to limit transplanting
shock. Hardiness can be developed by reducing the growth of the trees which may require
lower temperatures, light, and water. Full dormancy and hardiness are not required for
seedlings outplanted in late June or July, but to avoid stem breakage during the handling of
the seedlings it would be helpful to partially harden them off so they are not as succulent and
tender.
For container seedlings you need to keep the growing medium between field capacity
(standing water at the surface) down to 70 percent of field capacity. As the seedlings grow,
much more transpiration occurs, and you may have to water as often as several times daily.
To initiate hardening of the seedlings it may be necessary to reduce water, temperatures, and
light.
It is best to water seedlings early in the day with a deep watering. This will stimulate better
root development and a better root to shoot ratio. During hot days, brief light misting during
peak afternoon temperatures can lower the risk of damage to seedlings by high temperatures.
Having a good mulch cover for the soil or container media can also improve water retention
and uptake by the seedlings.
HARVESTING AND TRANSPORT
When harvesting seedlings the following guidelines should be observed. (Ref.# 2 and #3)
1.
Be careful when lifting and handling the seedlings to make sure they
are not exposed to excessive warm temperatures or drying of the roots.
Preferred lifting temperatures (removal from the seed bed) should be
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in the 40 to 500 F range.
2.
Seedlings should be stored and transported in protective bags such as
polyethylene bags, waxed boxes, or open-ended peat moss bales. The
interior of the bags should be kept moist by adding wet sphagnum moss.
3.
Keep the seedlings cool or refrigerated during transport and while
awaiting planting. Once the seedlings have broken bud do not refreeze
them. (Storage temperature should be kept around 35 to 400 F)
The use of high tunnels in Alaska may also assist in
the production of high quality seedlings in nonheated plastic structures having lower cost per tree
than that produced in heated greenhouses. Living
tree sales are undergoing research and may prove to
be viable for our climate.
INTEGRATED PEST MANAGEMENT PRACTICES
Although commercial spruce tree seedling production does not currently exist in Alaska,
many woodlot managers, foresters and landscapers utilize some form of IPM practices.
Alaskan forests are relatively free of many major pests that persist in lower 48 forests,
however due to Alaska’s expansive spruce monocultures; the destructive pests that are present
have caused extensive damage. Spruce plantations in Alaska risk potential infestation and
damage by the following agents. Careful monitoring and prescribed pesticide applications can
provide control of damage and reduction of potential tree losses. In addition to insects and
disease found in Alaska, trees also can be damaged or destroyed by moose, vole, hares and
porcupines. These indigenous vertebrates should be considered when planting. Fencing,
arbor guard, and other exclusion practices will benefit new and established plantings
.
Browse damage at snowline from hares
Stem damage from moose predation
The quarantining of new plant materials and the monitoring of existing stands for newly
introduced pest species continues to provide timely information in helping to avoid damage
and subsequent reduction of valuable plantings. Thoughtful site selection for future stand
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development, combined with careful thinning and pruning practices add value to healthy
forest plantings.
DISEASES
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Damping Off
Spruce Needle Rust
Rhizosphaera Needlecast
Damping Off – (Pythium/Phytophthora): Although damping off syndrome can be caused by
either fungal infections or abiotic factors such as chemicals and fertilizers, their symptoms are
somewhat similar in that seedlings tip over at ground level (root collar). It is important to
monitor young seedlings for evidence of damping off syndrome and remove any dying or
dead seedlings in order to reduce the risk of further contamination. Fertilizer applications and
watering may need to be reduced if losses by damping off are not controlled. Contaminated
or moldy seedlots exhibiting high germination losses to damping off disease may need to have
the seeds treated with a 3% solution of hydrogen peroxide for four hours prior to germination
to increase seedling survival. In some cases, a preplant chemical treatment may be required to
minimize the effects of damping off disease.
Spruce Needle Rust (Chrysomyxa ledicola Lagerh.): This is a fungal disease that infests only
the current years’ spruce needles but requires an alternate host to complete its life cycle. The
infections are characterized by the presence of pale orange spore masses which erupt from the
needles. The spruce needle rust (SNR) has an alternative host, Labrador tea Ledum spp,
which must be present in the environment for the lifecycle of the rust organism to be
completed. Control of Labrador tea within the ground vegetation around the trees out to about
1000 feet will provide some protection from further infections. The SNR can cause trees to be
weakened and defoliation to occur but the infections are cyclical and dependent upon cool
moist conditions for spore formation. Control is possible by fungicides for high value trees or
seedlings where appearances are of concern.
Table 4. Chemical Options for Control of Spruce Needle Rust
Fungicide
Protect D/F
Product Rate
1-2 lbs./100 gal
a.i. Rate
2.4-4.8 lb/100 gal
REI
24 hours
Spruce Needle Blight or Needle Cast: There are three diseases in this class of needle fungal
infections that affect spruce needles: (Lirula macrospora (Hartig) Darker), (Lophodermium
picea (Fckl.) V.Hohn.) and (Rhizosphaera pini (Corda) Maubl.). Spruce needle cast or blight
is usually not fatal to trees unless there are several successive years of attack. Outbreaks
follow wet weather patterns that allow the spores to spread via rain splash. Infected trees are
often localized but if control becomes necessary, carefully timed applications of fungicides
have been shown to be effective. Nurseries may need to limit the time that the needles are
wet.
Spruce needle cast is a fungal infection that usually only appears on one year old needles,
however, older needles on trees under stress can also be infected. The infection actually
begins with an initial infection of the new-year’s growth of needles by spores which then
don’t become pronounced until after the needles are one year old. Symptoms usually first
appear on the tree’s lower branches and then progressively move upward in the tree. Black
14
fruiting bodies will appear as dark spots or patches on the underside of the needles. Fungicide
control of needle cast can be successful, but careful timing is required to apply the fungicide
just as the needles are starting to emerge after bud break. Delayed application of fungicides
will likely be much less successful in controlling the infection. Control may require planting
alternative tree species that are not susceptible to spruce needle cast.
Table 5. Chemical Options for Control of Spruce Needle Cast or Blight
Fungicide
Bravo Weather Stik
Kocide 2000
Protect D/F
Spectro 90 WDG
Product Rate
2-5.5 pt/A
1.5-3 lb/A
1-2 lbs./100 gal
1-2 lb/100 gal
a.i. Rate
1.5-4.125 lb/A
0.81-1.61 lb/A
2.4-4.8 lb/100 gal
0.9-1.8 lb /100 gal
REI
12 hours
24 hours
24 hours
12 hours
Note: Although rusts and needlecast typically attack older trees there is evidence to suggest
that they can be a problem in plantations and nurseries. A more detailed description of
spruce container diseases and insects can be found in Ref#6.
MITES & INSECTS
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Spruce Spider Mite
Spruce Budworm
Spruce Aphid
Spruce spider mite (Oligonychus ununguis): The presence of spruce spider mites is
indicated by yellow or bronzish stippling beginning near the needle bases. Infestations
usually begin on older needles of the lower branches and spread upward as the mite
population increases. Damaged needles may turn brown or reddish-brown. Fine webbing
may cover the needles and twigs. The actual spider mites are very small and vary in color
from greenish to orange, dark green or black, with orange legs. Spruce spider mites attack
many species of conifers. They are usually spread by wind. These mites are often found on
dusty roadside trees.
Table 6. Chemical Options for Control of Spruce Spider Mites
Insecticide
Insecticidal soap
Product Rate
2.5 fl oz/gal
a.i. Rate
0.16 lb /gal
REI
12 hours
Spruce Budworm (Lepidoptera: Tortridcidae; Choristoneura): This is a pest found
throughout Alaska. They feed on foliage and buds of true firs, spruce, and Douglas fir.
Mature larvae are green-brown and up to an inch in length. They destroy buds, new foliage,
cones, and seeds. They typically attack the newer needles but repeated infestations can result
in damage to older needles as well. Symptoms include defoliation or thinning of the upper
canopy of the tree. Brown caterpillars emerge in mid-May and begin feeding on new needles.
Large infestations show reduction in radial growth with top kill being common. Monitoring
population buildups through trapping and visual observation along with a timely application
of chemical controls if needed can be used to control defoliation and cone reduction.
Although this is not a common problem for seedling production in Alaska, it was felt that it
would be beneficial to include control measures for existing trees ranging from seedling to
fully mature. The present epidemic of eastern spruce budworm has caused considerable
concern for landowners that are interested in planting and growing spruce seedlings.
15
Table 7. Chemical Options for Control of Spruce Budworm
Insecticide
Biobit HP
Product Rate
0.25-0.75 lb/100 gal
a.i. Rate
0.145-0.436 lb/100 gal
Sevin SL
0.75 fl oz/1000 sq ft
0.02 lb/1000 sq ft
REI
4 hours
12 hours
Spruce Aphids (Homoptera: Aphididae; Elatobium abietinum ) and Spruce gall aphids
(Homoptera: Phylloxeridae; Adeligidae) are found in southeast Alaska up through the
Interior. Population increases are directly related to mild winter temperatures and available
soluble nitrogen. Stressed trees are more susceptible to damage, so with careful production
practices the populations could be kept at a reasonable level. Removal of galls from high
value trees is an efficient control method if done before adult emergence in summer.
Commercially available insecticides are also effective.
Table 8. Chemical Options for Control of Spruce Aphids
Insecticide
Product Rate
a.i. Rate
REI
Azatin XL
21 fl oz/A
0.04 lb/A
4 hours
Talstar
5-10 fl oz/A
0.025-0.05 lb/A
12 hours
Tempo
1.5-5.4 oz/100 gal
0.012-0.042 lb/100 gal
Till dried
Insecticidal soap
3-5 fl. oz gal
0.014-0.024 lb/gal
12 hours
0.078-0.156 lb/100 gal
12 hours
Endeavor 50WG*
2.5-5 oz/100 gal
*Do not apply more than 48 oz./A per year.
Note: A more comprehensive review of insects and diseases of Alaska tree species can be found in: Insects and
Diseases of Alaskan Forests, 2009. R10-TP-140. USDA Forest Service publication
REFERENCES
#1. Alden, J. December 4, 2003. Naturalization and Growth of Nonnative Conifers in
Alaska. A presentation at the Introduced and Invasive Species in Resource Management
Conference hosted by the Alaska Society of American Foresters in Fairbanks. p.19.
#2. Chastagner, G. (Editor). 1997. Christmas Tree Diseases, Insects, and Disorders in the
Pacific Northwest: Identification and Management. Washington State University Cooperative
Extension, 154 p.
#3. Dumroese, K., T. Landis, and D. Wenny. December 1998. Raising Forest Tree Seedlings
at Home. Idaho Forest, Wildlife, and Range Experiment Station, Contribution Number 860,
56 p.
#4. Landis, T.D.; Tinus, R.W.; Barnett, J.P. 1998. The Container Tree Nursery Manual.
Volume 6, Seedling Propagation. Agric. Handbook. 674. Washington, DC:USDA Forest
Service. 166 p.
#5. Landis, T.D.; Tinus, R.W.; McDonald, S.E.; Barnett, J.P. 1994. Nursery Planning,
Development, and Management, Vol. 1, The Container Tree Nursery Manual. Agric. Handbk.
674. Washington, DC: U.S. Department of Agriculture, Forest Service. 188#p.
16
#6 Landis, T.D.; Tinus, R.W.; McDonald, S.E.; Barnett, J.P. 1989. The Biological
Component: Nursery Pests and Mycorrhizae, Vol. 5, The Container Tree Nursery Manual.
Agric. Handbk. 674. Washington, DC: U.S. Department of Agriculture, Forest Service, 171p.
#7. Landis, T.D.; Tinus, R.W.; McDonald, S.E.; Barnett, J.P. 1992. Atmospheric
Environment, Vol. 3, The Container Tree Nursery Manual. Agric. Handbk. 674. Washington,
DC: U.S. Department of Agriculture, Forest Service. 145 p.
#8. Quarberg, D. and T.R. Jahns. 2000. Wet-towel germination test. UAF-Cooperative
Extension Service Publication # FGV-00249, p 1-4.
#9 Schopmeyer, C.S. 1974. Seeds of Woody Plants in the United States. Agriculture
Handbook 450. Washington D.C.: USDA Forest Service. 883 p.
#10. Wheeler, R.A. 2001. Managing Your Trees and Shrubs in Alaska – Part Two: Planting
Guide for Trees in Urban and Rural Alaska. UAF- Cooperative Extension Service,
Publication No. FWM-00114,
32 p.
#11 Wheeler, Robert A., and John N. Alden. April 1998. Producing High Quality Spruce
Seedlings for Southcentral and Interior Alaska. Alaska Extension Review 1997. 70 p.
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